Removal of scale from ferrous metals



United States atent 2,820,729 Patented Jan. 21, 1958 fine REMOVAL onSCALE FROM FERROUS METALS Benjamin F. Davis, Jr., Houston, Tex., andPaul H. Cardwell, Midland, Mich., assignors to The Dow Chemical Company,Midland, Mich, a corporation of Delaware No Drawing. Application August4, 1955 Serial No. 526,548

7 Claims. (Cl. 134-42) This invention concerns an improved method forremoving, from ferrous metals, scales comprising rust and/ or othercorrosion products, e. g. oxides or hydroxides of the metals. itpertains especially to the removal of such scales from inner surfaces ofboilers, heat-exchangers, and pipes, etc., for generating or handlingsteam at high pressures.

Such iron or steel equipment for the generation or handling of highpressure steam, i. e. steam at a pressure of 400 p. s. i. g. or above,undergoes corrosion and often becomes coated on the inside with a scalerich in oxides or hydroxides of the metal or metals present. The rate offormation or accumulation of the scale is dependent, of course, on thekind of ferrous metal employed and such equipment is often constructedof, or lined on the inside with, corrosion-resistant alloy steels suchas the so-called stainless steels comprising iron alloyed with lesseramounts by weight of nickel and/or chromium. However, the scale tends toform oraccumulate in the equipment regardless of the kind of ferrousmetal employed, i. e. regardless of Whether inner walls of the equipmentare constructed of ordinary iron, or carbon steel, or of acorrosion-resistant alloy steel. For efficient operation of theequipment it is important that the scale periodically be removed.

As indicated above, the scale formed in high pressure steam equipmentusually consists for the most part, on a weight basis, of oxides orhydroxides of the metal or metals present. The scale may, and sometimesdoes, include other solid ingredients such as calcium sulfate, orsulfates or other salts of the metal or metals of which the equipment isconstructed, but the other ingredients just mentioned are usuallypresent in minor amounts. Although similar scales rich in rust, or in amixture of oxides and/or hydroxides of iron and other heavy metals suchas nickel, chromium, or molybdenum, etc., often are formed on thesurfaces of ferrous metals in ways other than by contact with highpressure steam, and the method of the invention is applicable inremoving such a scale regardless of how it was formed, the scales justmentioned are different from the scales rich in calcium and magnesiumsulfates, carbonates or other metal salts, but often comprising minoramounts by weight of rust, which are deposited from water in pipe linesand on the inner surfaces of household water heaters or on the innersurfaces of boilers for the generation of steam at pressures lower than400 p. s. i. g. The last mentioned scales, rich in metal salts are notas readily removed from metal surfaces by the method of the presentinvention as are the scales rich in heavy metal oxides and hydroxides,e. g. rust, that are formed inside high pressure steam equipment.

Several methods for removing scales from iron or steel surfaces areknown and are commonly used. Mechanical removal of the scale isdisadvantageous in that it requires disassembly and reassembly of theboilers or other metal equipment. ployed for removal of the scales, richin metal oxides or hydroxides, from iron or steel surfaces, but usuallyresult inhibited aqueous acid solutions can be emin a small, butappreciable, amount of corrosion of the iron or steel parts from whichthe scale is removed. Since the extent and distribution of the corrosionoccurring during such removal of scale from the plates and tubes of ahonor or heat exchanger cannot readily be determined, repeated use ofinhibited acids for the removal of scale from equipment for the handlingof steam at high pressures is not desirable. it has been proposed toremove scales comprising metal oxides or hydroxides from inner surfacesof boilers or similar equipment by circulating an aqueous slurry ofgranules or particles of an ion exchange material, e. g. sodium zeolite,through the equipment. In tests of this method, it has been found thatusual ion exchange materials, such as the sodium form of a sulfonatedion exchange resin, which ion exchange materials are in the form of hardparticles or granules soaked with water, react very sluggisnly to loosenand remove the scale. Also, care is required to avoid formation insideof the boiler or other equipment of deposits of the insoluble ionexchange material. Such deposits of ion exchange material, if permittedto form in the equipment, may be as objectionable as the scale that isto be removed.

It has now been found that alkali metal salts of sulfohated resins whichare capable of being highly swollen to fragile jell-like bodies that arereadily broken into small soft particles by moderate agitation orstirring in water are effective in loosening and removing theaforementioned scale rich in oxides or hydroxides of heavy metals,especially of iron, from the surfaces of ferrous metals and that theyhave little, if any, corrosive action toward the metals, i. e. theircorrosive action, if any, is of about the" These soft, fragile,-

same order as that of water alone. highly water-swollen alkali metalresin sulfonates tend to remain dispersed or suspended in aqueous mediaand render the suspensions far more viscous than water alone. They reactmore rapidly to chemically absorb metal irons from the aforementionedscales than do either the hard granules of conventional cation exchangeresins in alkali metal salt form or the alkali metal resin sulfonatesthat can be dissolved or dispersed in water Without causing a tremendousincrease in viscosity of the resulting composition over that of wateralone. In fact, the effectiveness of alkali metal resin sulfonates inreacting with and loos ening the scale appears to be dependentprincipally upon the extent to which the resin sulfonates are swollen byand thicken water when added to and stirred with the water and to alesser extent upon the identity of the sulfonated resin itself. Forinstance, in tests of a series of lithium salts of sulfonated vinylaromatic resins, i. e. sulfonated polymers or copolymers of styrene, itwas found that the resin sulfonates which were most effective inremoving the aforementioned scale from steel surfaces were salts ofresin sulfohic acids which, when stirred with water to form aqueousdispersions containing 0.5 weight percent of the respective resins,formed such dispersions having viscosities of from to 400 cehtipoises at25 C. The lithium salts of resin sulfonic acids having this range ofthickening effects toward water were far more effective in removing thescale from steel surfaces than were lithium salts of resin sulfonicacids that had lesser or greater effects than just stated in thickeningwater.

The above-stated range of viscosity values was determined for aqueousdispersions of the resin sulfonic acids rather than the alkali metalsalts thereof. However, the alkali metal, e. g. the sodium, potassium,or lithium, salts of the resin sulfonic acids are dispersible in waterand possess thickening effects for the water which do not differ greatlyfrom those of the corresponding resin sulfonic acids. I

It has also been found that other alkali metal resin sulfonates, e. g.sodium, potassium, or lithium salts of sui- 1.9 fonated vinyl aromaticresins such as polystyrene, copolymers of styrene and vinyltoluene, andcopolymers of styrene and acrylonitrile, etc., were most effective forremoval of the scale when they were salts of resin sulfonic acids havingthe above range of thickeningeffects in increasing the viscosity ofwater and that such saltsof corresponding resin sulfonic acidshavinglesser or greater thickening actions toward water were lesseffective, or noneffective, in removing such scale. 7

It was further found that alkali metal salts of other kindsofresinsulfonic acids that similarly are highly swellable by water to formsoft, fragile gels and that can be dispersed by stirring in water tothicken the latterare also effectivetin reacting with and removing thescale. For instance, alkali metal salts of highly water-swellablesulfonated phenol-formaldehyde resins are effective ;for em a of t esc efr m e ro s metal Fro 'n these'results it is evident-that is thephysical P op r s, esp c al y e re at v hick ning acti ns to- W r at LQthe k l me al resi -sulfonate whichd termine forthe most parttheeffectiveness of.-alkali:mtal e n l t sf ng th iscaleandthatanyalkali metal salt of a resinsulfonic acid having the above1d6- scr e thk ing ion t w r water .can s tisfactorily be used. 'Iheidentityofthe-alkalimetalresin sulfonate appears to be less important than ,itsthickening action toward water in determining its CliQlIlYCnSSjfQFfl16scale removal.

The highly swellable alkali metal resin sulfonates which aresatisfactorily ,efifective in removing the scale from ferrous metalshave very little, if any, corrosive action toward the metals themselves,,i. ;e. the slight amount of corrosion-which occurs during treatment ofa ferrousmetal with an aqueousdispersionoof suchalkali metal resinsulfonate is about the same as results from an otherwise similartreatment of the metal with water alone. Accordingly, the highlyswellable ,alkali :metal resin sulfonates can be employed .to remove thescale from iron or steel surfaces without causing appreciable corrosionof the metal itself. This is of importance in removing scale depositsfrom boilers or other-metal equipment for generating orhandling steam athigh pressures.

It has further been ,found that highly swellable resin sulfonic acidshaving the above-stated range of thickening actions toward Water arenot, ofthemselves, rapidly corrosivetoward ferrous metalsand that they.are more rapidly reactive with the scalepto loosen and remove thelatter from the surface .of a ferrous metal than .are h .GOrrespondingalkali metal resin sulfonates. Their failure to cause rapid corrosion ofthe iron or steel is, presumably, due to the fact thatalthough theyare'highly absorptive of water and .are readily dispersible, -e. .g. ascolloidal or larger particles, in aqueous media, they are not trulysoluble in water. However, the invention is not restricted by this orany other theory in explanation of the results obtained. Since the resinsulfonic acids are strongly acidic, :they are not .as convenientlystored, shipped or handled as are the alkali metal salts thereof. Therapid scale-removing activity and substantially noncorrosive action-toward .ferrous metals of the highly' swellable resin sulfonic acidsmay be obtained by employing, for the scale removal, an aqueousdispersion of the highly swellable alkali metal resin sulfonate .andduring its use gradually adding, with stirring or other agitation, astrong mineral acid such as hydrochloric or sulfuric acid at a rate suchas to maintain the slurry at pH values between 2 and 7, preferablybetween 2.5 and 4.5, e. g. at a rate such that a considerable amount ofthe resin sulfonate remains in the form of metal salts thereof.

Resin sulfonates having the above-described necessary properties ofbeing highly swellable by water to the form of soft, fragile gels and ofbeing dispersible by stirring in Water to thicken the latter, andmethods of making the same, are known to the art. However, many of thewell-known resin sulfonates do not possess said properties. For instancethe sulfonated phenol-formaldehyde resins and'the sulfonated copolymersof styrene with ethylvinylbenzene and divinylbenzene which are wellknown for use as cation exchange resins are insoluble in, and onlymoderatelyswollen by, water, and both before and after being soaked withwater are in the form of hard granules or particles which have verylittle,-if any, effectinthickening, i. e. increasing the viscosity of, abody of water in which they are immersed. However, phenol sulfonic acidand formaldehyde can bechemically condensed with one another under theaction of acidic condensation catalysts to form resinous condensationproducts which are highly swellable'to soft gels by water, aredispersible in ;water..t.o thicken the latter, and which in their acidform, or preferably in the form of alkali salts thereof, can be used toremove scale from ferrous metals in accordance-with the method of theinvention. Polystyrene, or other vinyl aromatic resins, can besulfonated to form water-insoluble sulfonates that are not highlyswellable by, or readily'discersible in, water and are not suitableforuse in the present method; or they can be sulfonated under conditionssuch as to obtain highly swellable resin sulfonates which aredispersible'by stirringin waterto thickenthe latter and are well adaptedfor use in removing scale from ferrous metals by the method of theinvention; or they can in some instances be sulfonated under otherconditions such that the sulfonated resin products are trulywater-soluble, have only a moderate effect of thickening water in whichthey are dissolved and are not satisfactory for use in the method of theinvention. sulfonated vinyl aromatic resins having the necessaryproperties of being highly swellable to soft gels by water, anddispersible in water to thicken the latter, are most readily obtainableby feeding into admixture with one another a stream of chlorosulfonicacid, preferably diluted with an equal volume or more of a liquid.

polychlorinated lower aliphatic hydrocarbon such as carbontetrachloride, tetrachloroethylene, methylene chloride, or ethylenechloride,.and,a dilute, e. g. 3 weight .percent or less, solution .ofthe unsulfonated vinyl aromatic resin in such liquid polychlorinatedaliphatic hydrocarbon at rates such as to bring. the chlorosulfonic acidand theresin together .in proportions of at least 0.6, preferably from0.8 .to 2, molecular equivalents of the chlorosulfonic acid permolecular equivalent of monovinyl aromatic compound chemically combinedin the resin, whilemaintaining :the resulting mixture at reactiontemperature not higher than 35" C. and preferably from 15 to 30 C,

Other ,usual sulfonating agents such as concentrated SUI! furic acid,fuming sulfuric acid, or sulfur trioxide can be used in place ofchlorosulfonic acid to obtain suitable resin sulfonates, .butchlorosulfonic acid has been more convenient and satisfactory than othersulfonating agents for use in sulfouating vinyl aromatic resins to makevinyl aromatic resin sulfonates having the afore--. mentioned propertieswhich are required for use in the scale-rem val method of the invention.

Although any resin sulfonate which is highly swellable by water to forma soft. fragile gel and which hasthe hereinbefore-described thickeningaction toward water can be used in practice of the invention, sulfonatesof thermoplastic vinyl ar matic resins having such properties arepreferred. Examples of vinvl aromatic resins which may be sulfonated asdescribed above to obtain suitable sulf nates are the s lid thermplastic p lymers of styrene, vinyltoluene, and vinylxvlene; thecopolymers .of the compounds just named with one another; and thethermoplastic copolymers of a major amount by weight of one or more ofsaid com ounds with minor amounts of other polymerizable viriylidenecompounds such as acrylonitrile, or 'isobutylene; etc.

In applying the invention for the removal of scale from the innersurfaces of a high pressure steam boiler, one bl? more of the highlywater-swellable resin sulfonates effective as thickening agents foraqueous liquids, usually a highly water-swellable alkali metal resinsulfonate, and

preferably a lithium resin sulfonate, is stirred together with water toform an aqueous dispersion thereof. The 5 resin sulfonate dispersion ismore viscous than water and its viscosity varies in accordance with theconcentration thereof. It should be sufiiciently dilute to permitpumping the same. In most instances, it contains from 0.1 to 2 percentby weight of the resin sulfonate, but it may be of concentrations loweror higher than just stated. The highly swollen soft resin sulfonated maybe dispersed as colloidal particles or may be suspended in the water aslarger particles. The resulting dispersion is circulated, e. g. by meansof a pump, through the boiler. if desired, a strong mineral acid such ashydrochloric or sulfuric acid may gradually be fed into admixture withthe circulating aqueous mixture at a rate such as to maintain themixture at pH values of from 2 to 7, preferably from 2.5 to 4.5. Theaddition of a mineral acid speeds up the rate of removal of the scalefrom the boiler and can be accomplished without causing appreciablecorrosion of the metal parts of the boiler. However, in order to avoidcorrosion, the mineral acid should not be added in amount or at a rateexceeding that required for liberation of all of the resin sulfonic acidfrom its metal salts and the added acid should quickly and thoroughly bestirred into the aqueous dispersion. Addition of a mineral acid to thealkali metal resin sulfonate disper- 6 were testedv for efiectiveness inremoving iron oxide deposits or coatings from stainless steel testpieces. The resin sulfonic acids are characterized by the respective /2percent viscosity values which are given, each of which values is theviscosity in centipoises at 25 C. of an aqueous dispersion or mixtureformed by stirring one part by weight of a resin sulfonic acid in 199parts of water. Portions of the respective solid resin sulfonic acidswere dispersed in separate portions of water, each dispersion wasbrought to a pH value of 7 by neutralization with lithium hydroxide, andthe resulting lithium resin sulfonate dispersions were brought, e. g. bydilution with water, to the respective concentrations given in thetable. The lithium resin sulfonate dispersions thus formed wereindividually tested for efiectiveness in removing an iron oxide scalefrom a stainless steel test piece. Each such test piece was formed byspreading an aqueous paste of powdered Fe O over a face of a test piececomposed of a stainless steel comprising iron as the principalingredient alloyed with about 18 percent by weight of nickel and 5percent of chromium and baking the coated piece at a temperature of 250F. for 6 hours to form a scale of inch thickness thereon. In eachexperiment, such metal test piece having the scale thereon was immersedin a stream of one of the aqueous lithium resin sulfonate dispersions,which stream was heated at 175 F. and circulated over the test piece ata linear flow rate of 7.8 centimeters per second. in some, but not all,of the experiments the aqueous resin sulsion is not required for removalof the scale from the f9nat dispersion attacked loosened and removed a gboiler, i. e. the aqueous alkali metal resin sulfonate disslqerableamount of the A large of persion, although less rapidly reactive, is ofitself effective Oxlde thus remov.ed was the form dlsper slon fortherpurposa sumably of the iron resin sulfonate, in the circulating Thescale removal may be accomplished by circulathquor' The p was i i in thecirculating ing the aqueous resin sulfonate solution through the streamof the resin sulfonate dispersion for 2 hours and boiler at roomtemperature, but takes place more rapidly then removed. .i was thenInspected i the percent at elevated temperatures. The resin sulfonatedispersion of the scale lmtially Present thereon whlqh had .been isusually heated to above room temperature and removed was estimated. Therates at WhlCh stainless usually to temperatures in the order of from 0to steel of the above-mentioned composition becomes cor- 250 F. or abovewhile being circulated through the f f by hot water alone and by freshheated aqueous 1 The Scale removal Operation can usually be lithiumresin sulfonate dispersions of the kinds and concarried out in a few, e.g. from 2 to 10 hours, but in centrations employed in theabove-described experiments instances in which a heavy scale deposit ito be rewere determined as follows. An uncoated plate of the rnoved,longer times may be required. After loosenstainless steel was weighed,then immersed in the liquid mg or removing the scale 1n the manner ustdescribed, which was heated at 175 F. and circulated over the test 2?boiler 18 3 3 flushed Wlth a vlgorous flow of water. plate for 16 hours.The metal plate was then removed, 3512 ffi dy p t i 3 E dried, andweighed. The corrosion rate, expressed as me 0 1 6 can 6 if pounds ofmetal lost by corrosion per square foot of moving scales rich in rust orother metal oxides or hydmxidgs from other kinds of i on or S e l equpmen initial metal surface per 24 hours, was calculated from e. g. fromheat exchangers or pipe lines, etc. 2 i s-conecm-d and i t, glven m TheThe following examples describe ways for practice of ta 6 1 mm and glYes/2 Per-cent vlscoslty Value the invention and illustrate certain of itsadvantages, but each resm sulfomc i glves l percent by are not to beconstrued as limiting the invention weight of the corresponding lithiumresin sulfonate in EXAMPLE 1 the aqueous dispersions thereof which weretested for I scale removal. It also gives the percent of the scale ini-L1th1um salts of several vinyl aromatic resin sulfonic ti lly presentwhich is estimated to have been removed acids, named and characterizedin the following table, in each Sca e removal experiment.

Table I Resin sulfonate Scale removal and corrosion tests Test No. 95percent vis Percent of Li resin sulfonate in Percent Corrosion rate,Kind, 1. e. a sulfonate ofcosity of dispersion tested of scale lbs/sq.fin/day its acid removed form Polymer of vinyltolucne 25 Not determinedPolystyrene 25 0.000007. Copolymer of 50 wt. percent styrene 0.000076.

and 50 percent vinyltoluene. Polystyrene 33 0.000079. d 0.5 0 00.000025. None; 1. e. corrosion test using 0.000045.

water as the liquid.

7 The corrosion rates in4the itable :in'dicate that the: aqueouslithiunr res'in sulfonat'ed: dispersionswere not greatly more"corrosive,anct in:flsome instances were less corrosive,- than water' I alonetoward' the m'etal. The table indicates that the' lithiurni :salts of.resin 1 sulfonic acids having /2 percent viscosity values between "100and 4,000 centipoises are the' most effectivehin removi-ng the.scalea'nd that-the effectiveness'ofiscaleflremoval decreases as the /2percent viscosity" values of the corresponding resinsulfonic acidsiapproa'ch or reach-the limitingvalu'es just stated. 7

EXAMPLE 2 *A- number of other resin sulfonates were tested: forelfectiveness in removing-an iron oxide scale: from: plates of stainlesssteel'. Excepttor theikinds of Iesinsulfonates employed; the procedureincarrying out. the tests was sim'ilar-to that described imExample 1.Table II :identifies each' resin sulfonate and gives theweightpercent'concentration of the same in the aqueousxiispersionthereof. The table'givesthe /2 -pe'rcent' viscosity valuefor thecorresponding resin'sulfonieaeid and 1 gives the percent of scalewhichis estimated T to have been removed from the test plate; by action oftheaqueous resin sulfonate dispersion. is In 'some' instance the /2percent-viscosity values. of the resin sulfonicids inwater were notdetermined directly; but were estimated on a basis of viscositiesmeasured for aqueous dispersionsof 'theresin sulfonic acids in otherthan /2 percent concentrations The table indicates which of said values1 are estimated. 1 The esti mated v'alues' may involve -fa-i-rly largenumerical errors, but'are 'believed to be of suificient accuracy for'the present purpose.

- Table -II Resin sulfoii'ate Scale removal test Test per- Salt of theresin -N 0. cent of sulfonic' acid Percent Sulfonate oiviscosity ofscale of acid 7 removed form' "Kind of Percent -salt cone.

1 Polystyrene 5-20 Na'salt.- 0.5 2---. ;;d0 150 do 0.5 o 400 do 0.17Copelymer oistyrene 1,-360 Lisalt--. 0.09

and smaller arnt of t acrylbnitrile. v 5 Polystyrene 3000- Na salt I0.07 33 6 Copolymer of about 1 4,000 Li-salt 0.2 10

99.8 wt. percent 'vinyltolirene, 0.1

percent ethylvinylbenzene and 0.1 percent divinylbenzene.

Estimated.

" EXAMPLE 3 p This example illustrates'the' effect of adding a mineralacid to an aqueous dispersion of a highly 'water-swellable alkali metalresin sulfonate dispersion during use of the latter for removal of scalefrom the surface if a ferrous metal. In each of several experimentsthere was employed a'test'plat'of a' stainless steel comprising iron as-thc principal ingredient 'alloyed 'withabout l8 weight percent ofnickel "and 8 'percentof' chromium, which test plate had on one of thefaces thereof a tightly adhering scale having acomposition difi'erentfromthatof the scale on the test plates which were used in theexperiments of Examples 1 and 2. The test plates which were-employed inthe present experiments were each prepared by coating one face of astainless steel plate with an aqueous paste of a powdered mixture of 40weight percent Fe O "15 In eeachexperime'ntsuchcoated plate was:immersed in a.

streamnotg 'a liquid which was heated at a temperature-of L75.Fe.and'wascirculated over the coated face of theplatezat a linear.flowrate =.of 7.8 centimeters :per second The composition oi the;liquidwas changed -at;.least' to.-

some-extent: fr'omzone experiment -to:another. In "one .of-

the 'experimenta watenalone was the-:heat'ed liquidwhich.

was circulated over aftest plate. lnanother experiment; theliquid'wasvan aqueous dispersion 'of a lithium resin sulfonatev in; 0.25tweightzpercent-concentration-nvhich.

lithium resin sulfonate was sirnilarwin' kind -tmthatremployednin'run 3of the: TableI. In: another iof theiexsimilarT-lithium resin. sulfonatedispersion was initially employed; butduring circulation o f the heateddispersion, over a test pla'tehaving the scale-deposit thereon, sulfuricacid'wa'saddedas necessary to maintain the dispersion at a-pH value'of2.5. In each of the experiments,'-'the test plate, I initially bearing'the scale, was: immersed in the liquid' stream for the time indicatedin TableIII. 'Itwas then rern'oved and examined. From the examinationthe percent'* of f the scale, initially 'presenton the test plate,

which had been removed'by the treatment was estimated. Table 5 IIIindicates which of the above-described liquidsor procedures was used inthe respective experiments and The-table also gives=the percent "of thescale which isestimated to have been removed from a test plate ineachexperiment.

p Table [II n 'Time (if Percent v No. identification of liquid tested-immerof scale" 7 sion, hrs. removed 2 i Z '1 2- "Li'resin sulionatedispersion having pH of 7 3 20 3 Li resinv sulfonate dispersioninitially 2% 25' brought to pH of 2.5, but pH rose to 5 in 1st hour oftest. v V v I 4-.. Li resin-sulfonate dispersion maintained a 6 atpH of2.5throughouttest.

In a further experimenh an uncoated. test plate, of. known weightanddimensions and of the kind employed intthe experiments of Table lli,was immersed. in arstreamnof liquid, initially: consistingof the 0.25.percent lithium resin sulfonatedispersion, for' a measured periodtoftime. Throughoutsaid period, sulfuric. acid was added as necessary tomaintain. theidispersion .at a..pH waluesof' 2.5 ai1d the dispersionwasslheaterh to 1-75. .and circulatedatthe rate stated above. The. platewas then removed from the liquid, dried, and weighed to determine theamount of metal: lost by corrosion. #From" the data thus 'dbtained, the:ratetot icorrosion i of the' metal plate by theaqueous dispersion underthe conditions just stated was calculated to be 0.000065 pound persquare foot of initial surface area per 24 hours- EXAMPLE 4 This exampleillustrates use of an. aqueous dispersion of a lithium salt of a highlywater-swellable phenolformaldehyde resin sulfonic acid in practice ofthe invention. The lithium resin sulfonate dispersion was prepared inthe tollewi-ngm-anner. A-mix-ture of 200 grams percent Of Fe Og,'-25percent ofsiO and 20 percentiof I.

ofphenol andwfiiltl'gramsofxsulfuricacid of 98 percenticoncentration-was preparedgandmaintained for 2 hours, :at atemperature. oiapprbximately 35 F. The mixture was then'brought' toa'temperature "of" F. and was .stirredandmain'tainedatabout'80? F. .foi'22 hours. The mixture was next neutralized to a pH value of 7 by"treatmentwith'nn"aqueous calcium hydroxide suspension. The calciumsulfate which was thereby formed and precipitated was removed byfiltration, washed with water, and the washings were added to thefiltrate. The latter was then evaporated under vacuum at a temperatureof about 120 F. until the residual solution contained about 50 percentby weight of water. Lithium sulfate was added to the residual solutionin amount suflicient to precipitate remaining calcium ions as calciumsulfate and to convert the sulfonated phenol product to its lithiumsalt. The precipitated calcium sulfate was removed by filtration and thefiltrate was evaporated to obtain the lithium phenol sulfonate as asolid residue which was dried in an oven at 200 F. A portion of thelithium phenol sulfonate was dissolved in an aqueous formaldehydesolution of 37 weight percent concentration to form a solutioncontaining equimolecular amounts of the lithium phenol sulfonate andformaldehyde. To the resulting solution there was added, as acondensation catalyst, an aqueous sulfuric acid solution (formed bydiluting one part by volume of 98 percent sulfuric acid with 10 parts ofwater) in amount containing 0.32 molecular equivalent of sulfuric acidper mole of the formaldehyde. The mixture thus formed was heated at 180F. until it had thickened to an extremely viscous, barely fiowable body,i. e. until on turning the reaction vessel on its side the resinmeniscus shifted only slightly in 10 seconds. The mixture was thencooled and diluted with water to form an aqueous dispersion containing10 percent by weight of the resinous product. This dispersion wasneutralized with lithium hydroxide to a pH value of from 5 to 6. Aportion of the aqueous lithium resin sulfonate dispersion thus formedwas diluted with a further amount of water to a point at which itcontained 5 percent by weight of the resin sulfonate. The 5 percentresin sulfonate dispersion was far more viscous than water, but, wasreadily flowable. It Was tested to determine its efiectiveness inremoving an iron oxide scale deposit from the surface of a stainlesssteel plate. Except for the kind and concentration of the resinsulfonate dispersion employed, the procedure in carrying out thisexperiment on the removal of scale was similar to that employed in theexperiments on scale removal which are described in Example 1.Approximately 50 percent of the scale initially present on the stainlesssteel test plate was removed by the treatment with the aqueous lithiumphenol-formaldehyde resin sulfonate dispersion.

We claim:

1. A method for the removal of a scale, rich in oxides or hydroxides offerrous metals, from the surface of a ferrous metal, which methodcomprises contacting the scale with a stream of a flowable liquidaqueous dispersion of a resin sulfonate, which aqueous dispersion has apH value of from about 2 to about 7, and which resin sulfonate initiallycomprises an alkali metal salt of a resin sulfonic acid that is highlyswellable by water to the form of a soft, fragile gel and is dispersibleby stirring together with water and forms with water an aqueousdispersion that, when of 0.5 weight percent con centration, has aviscosity of from about 100 to about 4,000 centipoises at 0., wherebyscale is removed from the metal and is dispersed in the liquid, andthereafter removing the ferrous metal and the aqueous resin sulfonatedispersion out of contact with one another.

2. A method, as claimed in claim 1, wherein a deposit of the scale isremoved from surfaces of stainless steel equipment by contacting thescale with a stream of a flowable liquid aqueous dispersion of an alkalimetal salt of a vinyl aromatic resin sulfonic acid, which aqueousdispersion has a pH value of from about 2 to about 7,

10 and which vinyl aromatic resin sulfonic acid is highly swellable bywater to the form of a soft, fragile gel and is dispersible by stirringin water and forms with water an aqueous dispersion which, when of 0.5weight percent concentration, has a viscosity of from to 4000centipoises at 25 C., and heating the stream of the aqueous resinsulfonate dispersion at temperatures between 100 and 250 F. while incontact with the scale, maintaining the equipment in contact with thestream of the liquid resin sulfonate dispersion until a substantialportion of the scale has been removed from the equipment, and thereafterremoving the aqueous dispersion, comprising removed scale, from contactwith the equipment.

3. A method, as claimed in claim 2, wherein the scale is one rich iniron oxide and the aqueous dispersion is a dispersion of a lithium saltof the vinyl aromatic sulfonic acid in water.

4. A method, as claimed in claim 2, wherein the scale is one rich iniron oxide and the aqueous dispersion is a dispersion of a sodium saltof the vinyl aromatic resin sulfonic acid in water.

5. A method, as claimed in claim 1, wherein a deposit of the scale isremoved from surfaces of stainless steel equipment by contacting thescale with a stream of an aqueous dispersion of the resin sulfonate inthe form of an alkali metal salt thereof, and during such contact addinga mineral acid to the dispersion in amount such as to bring thedispersion to pH values below 7 and above 2, whereby scale is removedfrom the equipment and becomes dispersed in the stream of liquid, andthereafter removing the aqueous dispersion, comprising removed scale,from contact with the equipment.

6. A method for the removal of a scale, rich in oxides or hydroxides offerrous metals, from the surface of a stainless steel, which methodcomprises contacting the scale with a stream of a liquid aqueousdispersion of a lithium salt of a vinyl aromatic resin sulfonic acid,which vinyl aromatic resin sulfonic acid is highly swellable by water toform a soft, fragile gel and can be dispersed by stirring in water toform an aqueous dispersion of 0.5 weight percent concentration having aviscosity of between 100 and 4,000 centipoises at 25 C., and during suchcontact adding a mineral acid to the dispersion in amount such as tobring the dispersion to pH values below 7 and above 2, whereby scale isremoved from the equipment and becomes dispersed in the stream ofliquid, and thereafter removing the aqueous dispersion, comprisingremoved scale, from contact with the equipment.

7. A method for the removal of a scale, rich in oxides or hydroxides offerrous metals, from the surface of a stainless steel, which methodcomprises contacting the scale with a stream of a liquid aqueousdispersion of a sodium salt of a vinyl aromatic resin sulfonic acid,which vinyl aromatic resin sulfonic acid is highly swellable by Water toform a soft, fragile gel and can be dispersed by stirring in water toform an aqueous dispersion of 0.5 weight percent concentration having aviscosity of between 100 and 4,000 centipoises at 25 C., and during suchcontact adding a mineral acid to the dispersion in amount such as tobring the dispersion to pH values be-' low 7 and above 2, whereby scaleis removed from the equipment and becomes dispersed in the stream ofliquid, and thereafter removing the aqueous dispersion, comprisingremoved scale, from contact with the equipment.

References Cited in the file of this patent UNITED STATES PATENTS2,674,523 McDonald Apr. 6, 1954

1. A METHOD FOR THE REMOVAL OF A SCALE, RICH IN OXIDES OR HYDROXIDES OFFERROUS METALS, FROM THE SURFACE OF A FERROUS METAL, WHICH METHODCOMPRISES CONTACTING THE SCALE WITH A STREAM OF A FLOWABLE LIQUIDAQUEOUS DISPERSION OF A RESIN SULFONATE, WHICH AQUEOUS DISPERSION HAS APH VALUE OF FROM ABOUT 2 TO ABOUT 7, AND WHICH RESIN SULFONATE INITIALLYCOMPRISES AN ALKALI METAL SALT OF A RESIN SULFONIC ACDI THAT IS HIGHLYSWELLABLE BY WATER TO THE FORM OF A SOFT, FRAGILE GEL AND IS DISPERSIBLEBY STIRRING TOGETHERE WITH WATER AND FORMS WTIH WATER AN AQUEOUSDISPERSION THAT, WHEN OF 0.5 WEIGHT PERCENT CONCENTRATION, HAS AVISCOSITY OF FROM ABOUT 100 TO ABOUT 4,000 CENTIPOISES AT 25*C.,WHEREBYSCALE IS REMOVED AFTER REMOVING THE FERROUS METAL AND THE AQUEOUSRESIN SULFONATE DISPERSION OUT OF CONTACT WITH ONE ANOTHER.